1. Field of the Invention
The present invention relates generally to a method for disinfecting poultry and other food animals, and, more particularly, to a method for reducing pathogens in the gastrointestinal tract of a live animal prior to slaughter.
2. Description of the Related Art
Fresh food animal products, including poultry, are susceptible to contamination by microorganisms that contact meat surfaces immediately after slaughter and evisceration, including organisms in the gastrointestinal tracts which can be transferred during processing. Contaminating microorganisms include bacteria such as Salmonella and Campylobacter species, Listeria monocytogenes, Escherichia coli and other coliforms, and other enteric organisms. Once bacteria such as Salmonella contact tissue surfaces, they rapidly attach and are difficult to remove even with chlorine disinfectant permitted for use in poultry sprays and chill tanks. In beef processing, for example, a particularly virulent strain of E. coli, denoted O157:H7, reportedly contaminated hamburger meat sold by a fast-food chain and caused several deaths in the U.S. in 1993. Food poisoning from other
The problems created by Salmonella bacteria in poultry products are particularly noteworthy. Currently, Americans spend approximately $20 billion annually on poultry products, consuming about 80 pounds per capita. Approximately 35% to 45% of poultry reaching U.S. consumers is contaminated with Salmonella species. Improper cooking and physical transfer of the bacteria to food handling surfaces and thereafter to other foods result in the spread of the microorganisms, causing gastrointestinal disorders and, in some cases, death.
Breeders, hatcheries, feed ingredient suppliers, farms, processors, and distributors have all been implicated as contributors to Salmonella contamination in chickens and turkeys (Villarreal, M. E., et al., J. Food Protection 53: 465-467 (1990)). Contamination of but a few birds can lead to broader range contamination of other birds and cross-contamination to carcasses. Bacterial proliferation and other signs of spoilage can be delayed by refrigeration, but there is a limit to the degree of refrigeration that can be imposed on meat products, short of freezing the meat, and some bacteria such as psychrophiles can survive and even flourish at temperatures approaching the freezing point. It is thus preferable to control and destroy Salmonella and other microbial contaminants during processing to reduce the initial number of organisms on the meat.
Poultry processing is similar to the processing of other meat animals. Briefly summarized, caged birds arrive by truck at the processing plant. Typically, the birds are not fed for at least one to four hours before slaughter to allow the bird's intestinal tract to clear, thereby lowering the risk of fecal contamination during subsequent processing. The birds are hung by their feet on shackles in a dressing line, stunned and bled via throat cuts. After bleeding and while still hung, the birds are scalded, plucked and transferred to an evisceration line, where they are manually or mechanically eviscerated, inspected and spray-washed. The spray may contain chlorine as a disinfecting agent. Historically, the last step of the process has been chilling in a chill tank, by movement through a counterflow of cold water. The carcasses must reach an internal temperature of 5° C. or below, which usually takes about 45 minutes to one hour in a typical many-thousand gallon tank. After reaching this temperature, the carcasses are packaged or further cut into parts, and refrigerated or frozen.
Salmonella and other organisms can survive the scalding process, which involves temperatures of about 50° C. to 58° C. Though cross-contamination can occur during any stage of processing, the major problems arise during and after evisceration when microorganisms are freed from the intestinal tract and transferred to other tissue surfaces. When carcasses are placed in the chill tank, organisms and unremoved viscera and visceral contents enter the water and can come in contact with other carcasses.
The U.S.D.A. and F.D.A. allow the use of chlorine in the water, up to 50 parts per million (ppm), to destroy some of these organisms. Upper range chlorine levels transfer to the air and can irritate factory workers, so lower levels, e.g., 20 ppm, are typically employed. This compromises antimicrobial effectiveness, as does organic matter and debris that accumulate in water and consume available chlorine. Indeed, even the upper allowable chlorine levels cannot eliminate or significantly reduce pathogenic organisms. In addition, chlorine in process waters has a tendency to react with a variety of organic materials, both from water and from poultry, to form a series of chloro-organic molecules, e.g., trihalomethanes and chloramines, that have been implicated as mutagens and carcinogens.
Chlorine dioxide, which is less reactive with water components such as ammonia and nitrogen compounds, has been considered as an alternative disinfectant to chlorine in poultry processing. Chlorine dioxide can significantly reduce Salmonella and other unwanted microbial contaminants of meat surfaces, and at levels in water which are approximately one-seventh of that required for chlorine to achieve comparable effects.
Though chlorine dioxide has also been found to react with fewer amino acids than does chlorine (3 rather than 18), there is increasing evidence that the reactions cause undesirable effects on poultry surfaces. For example, it has been observed that chlorine dioxide, at the 1.4 ppm level in chiller water, was effective in reducing many bacteria and caused no detectable off-flavors on treated broilers, but the skin of the chickens was lighter in color than control carcasses, and the normal pinkish-white appearance had changed to grayish-white. Use of chlorine dioxide was curtailed in poultry processing as a result of sporadic retail complaints about “bleached” or old-looking carcasses. Moreover, subsequent chlorine dioxide experiments resulted in periodic episodes of severely discolored (blue-black) birds and random poor bacteriocidal efficacy.
Irradiation was approved by the U.S. government as an alternative antimicrobial treatment. However, irradiation appeared to not be viable for most poultry processors due to the high capital plant cost, high operating costs, and the additional cost of transporting carcasses to such facilities. Irradiation may also pose occupational risks to poultry factory workers.
Regulatory authorities in the U.S. have also approved the use of acidified chlorite/chlorous acid antimicrobial solutions in chiller tanks, as well as the direct application of such solutions to the defeathered/eviscerated carcasses immediately prior to their immersion in the chiller tanks. This results in the destruction of surface pathogens on individual carcasses, thereby reducing or eliminating their numbers so that they cannot subsequently contaminate the chiller waters and other non-contaminated carcasses. The application of these chlorite/chlorous acid solutions may be either by separate immersion of each poultry carcass in the liquid germicide solution, or by spray application. Typically, when these solutions are used to disinfect the surfaces of red-meat carcasses, following evisceration, they are applied as sprays.
For example, the application of acidified chlorite/chlorous acid antimicrobial solutions, for removing bacteria from poultry and other meats is the subject of U.S. Pat. Nos. 5,389,390 and 6,063,425. More specifically, U.S. Pat. No. 5,389,390 discloses a method for disinfecting a meat carcass by application of an aqueous solution containing from about 0.001-0.2% of a metal chlorite and a sufficient quantity of an acid to adjust the pH of the aqueous solution to about 2.2-4.5 and to maintain the chlorite ion concentration in the form of chlorous acid to not more than about 35% by weight of the aqueous solution. U.S. Pat. No. 6,063,425 discloses a method for disinfecting a meat carcass by spray application of an aqueous solution containing from about 0.05-0.12% of a metal chlorite and a sufficient quantity of an acid having a first pKa of from about 2.0-4.4 to adjust the pH of the aqueous solution to about 2.2-4.5 and to maintain the chlorite ion concentration in the form of chlorous acid to not more than about 35% by weight of the aqueous solution, wherein the molar ratio of the acid to metal chlorite is at least equal to the first pKa of the acid multiplied by the grams/liter concentration of metal chlorite in the aqueous solution.
In addition, various pre-slaughter methods of controlling the amount of pathogens in the gut of a live animal have been approved, such as the use of competitive exclusion cultures and antibiotics. More recently, the oral administration of sodium chlorate solutions to live animals, particularly cattle, prior to slaughter to reduce the amount of certain pathogens in the gut, specifically E. coli and Salmonella, has been proposed (U.S. Pat. Nos. 6,475,527 and 6,761,911 to Anderson et al.; Anderson, R. C., et al., J. Food Protection 63: 1038-1042 (2000); Callaway, T. R., et al., J. Food Protection 66: 194-199 (2003); and Callaway T. R., et al., Foodborne Pathogens and Disease 1:59-63 (2004)). Similarly, U.S. Pat. No. 5,830,511 to Mullerat discloses the oral administration of pH-buffered, redox-stabilized compositions comprising halide and oxyhalide ions, such as a mixture of chlorite, chloride and chlorate ions, wherein the pH of the composition is in the range of 7.5-13. However, such chlorate solutions are only effective against certain pathogens, namely pathogens possessing respiratory nitrate reductases, and, accordingly, do not offer broad spectrum antimicrobial protection.
Accordingly, although there have been advances in the field, there remains a need for improved, effective and economical method for removing Campylobacter, Salmonella and other unwanted microorganisms from poultry and/or other food animals. The present invention addresses these needs and provides further related advantages.